Missing output from pyserial

Question

I am reading from the serial port using the following code:

z1baudrate = 115200
z1port = '/dev/ttyUSB11'
ser = serial.Serial(z1port, z1baudrate, timeout=0, parity=serial.PARITY_NONE,

                    stopbits=serial.STOPBITS_ONE, bytesize=serial.EIGHTBITS)
while True:
    queue = ser.inWaiting()
    if queue > 0:
        data = ser.read(1000)
        print data
    time.sleep(.2)

I am supposed to get this result printed every few seconds

bbbb::0000:0:0:00 2412 7 -1 250 -58 108 0 2398 # output 1 
bbbb::0000:0:0:00 2475 4 1 264 -46 106 1 2423 # output 2

but instead, I occasionally receive incomplete output like

bbbb::0000:0:0:00 # sometimes broken into 2 lines
2412 7 -1 250 -58 108 0 2398 # line 2
bbbb::0000 # sometimes a part of the output is missing like this 
bbbb::0000:0:0:00 2475 4 # or like this. Length is variable!

What is the problem? Is it a synchronization issue? How do I fix this?

J. P. Petersen · Accepted Answer · 2016-04-06 07:21:14Z

1

It is a combination of the sleep and print statement. The program might sleep while a sentence is being received, and the when the print command is used, it will write a new line, each time.

Try this:

import sys

z1baudrate = 115200
z1port = '/dev/ttyUSB11'
ser = serial.Serial(z1port, z1baudrate, timeout=0, parity=serial.PARITY_NONE,

                    stopbits=serial.STOPBITS_ONE, bytesize=serial.EIGHTBITS)
while True:
    data = ser.readline()
    sys.stdout.write(data)

edited Apr 6, 2016 at 7:21

answered Apr 5, 2016 at 11:45

J. P. Petersen

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7 Comments

J. P. Petersen Over a year ago

I would also try to avoid using the sleep in a loop like this. You should maybe look into the readline from pyserial for this.

Ahmed Al-haddad Over a year ago

How about removing the sleep, will it work? I am currently testing your answer

Ahmed Al-haddad Over a year ago

And if I use readline, then how much should I set the timeout?

Ahmed Al-haddad Over a year ago

I am testing the readline now because the sys.stdout didn't workout. I however got a few times more than one line together like this as the output

bbbb::0000:0:0:00 2412 7 -1 250 -58 108 0 2398  bbbb::0000:0:0:00 2475 4 1 264 -46 106 1 2423#  I have two lines together as the output!

This may be due to the fact that I receive the output at random times sometimes, but how to eliminate this?

J. P. Petersen Over a year ago

Did you remember to import sys when using sys.stdout.write?

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